In making field-effect transistors (FET's) it is desirable to achieve very small and precise channel lengths to improve the high frequency operation. Furthermore, it is advantageous to minimize the feedback capacitance from the drain to the input gate electrode.
It has been known heretofore to carry out successive diffusion steps through a single mask and to control the diffusion process so that the boundary of the second diffusion will closely approximate the boundary of the first and will leave a thin channel between the second diffusion region and the layer in which the first diffusion takes place. However, the reduction of channel length due to the depletion layers still affects the equivalent channel length.
Accordingly, it is an object of the present invention to provide a metal-oxide-silicon type (MOS type) FET of the tetrode type with precisely controlled channels of very small dimensions.
It is another object of the present invention to provide a tetrode MOS type FET having minimum feedback capacitance between the drain and the input gate.
It is a still further object of the invention to provide an MOS type FET having improved high frequency performance.